The 3rd Generation Partnership Project (3GPP) oversees and governs 3rd Generation (3G) networks, including 3G Long Term Evolution (LTE) networks. 3G LTE provides mobile broadband to User Equipment (UEs) within the 3G LTE network at higher data rates than generally available with other networks. For example, the air interface for 3G LTE, Evolved Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access Network (E-UTRAN), utilizes multi-antenna and multi-user coding techniques to achieve downlink data rates of 100 s of Mbps and uplink data rates of 10 s of Mbps.
In LTE, user mobility is controlled by the network with assistance from the UE. Handover decisions, as well as the choices for the target cell and technology (when applicable), are made by the current serving eNodeB (equivalent to Base Station in 2G/3G network) based on measurements made by the eNodeB, and based on measurements reported by the UE to the eNodeB. Due to the nature of E-UTRAN, the number of packets buffered before scheduled transmissions occur may not be negligible. For that reason, packet forwarding mechanisms may be used (when applicable) between a source node and a target node so as to limit packet loss during handover from the source node to the target node.
Due to various delays, e.g., those caused by the forwarding process, the target node may receive forwarded data packets after receiving post-handover data packets. Such delays may cause the target node to deliver data packets to the UE out of order. Procedures currently exist to guarantee in-order packet delivery to the UE during handover of a UE between network nodes within the same Radio Access Network (RAN) and/or associated with the same Radio Access Technology (RAT). However, because no such procedures exist for handover of a UE between network nodes associated with some RATs, i.e., handover from 3GPP to HRPD (High Rate Packet Data), there is a risk of out-of-order packet delivery.